Java Intro

Strings “This is a string.” –Enclosed in double quotes “This is “ + “another “ + “string” –+ concatenates strings “This is “ “ string” –+ can also concatenate numbers and strings

Escape Sequences Same as in python –\t tab –\n newline –\” double quote –\\ backslash

Variables Unlike python, Java is strongly typed –You MUST specify the type of each variable Numeric primitive types –int,long, float, double

Examples int age; double cost; int x = 5; double a = 9, b = 9.5; x=b; //COMPILATION ERROR age = 10.6; //COMPILATION ERROR

Other Primitive Types char –A single character enclosed in single quotes –char first_initial = 'S'; boolean –true/false –boolean isPair = true;

Constants final keyword prevents changing value of variable –final double TAX_RATE =.0825;

Expressions +, -, *, /, % Same precedence as python

Expressions ++ = increase by 1 –int i = 0; –i++; //add one to i -- = decrease by 1 –int i = 10; –i--; //subtract 1 from i pre/post increment –int total1 = ++i; –int total2 = i++;

Data Conversion Assignment conversion –assign value of one type to variable of another type –OK for widening conversions int i = 5; double d = i;

Data Conversion Promotion –operators automatically convert operands –double a = 5.0; –int b = 6; –double result = a/b;

Data Conversion Casting –programmer explicitly specifies –specify type in parens –double d = 9; int x=(int)d;

Keyboard Input The Scanner class import java.util.Scanner; Scanner scan = new Scanner (System.in); scan.nextLine() scan.nextInt() scan.nextDouble()

import java.util.Scanner; public class Tax { public static void main(String[] args) { //A program to calculate tax and total cost for an item. //constant rate of taxation final double TAX_RATE =.0825; Scanner s = new Scanner(System.in); System.out.println("Enter item cost: "); //ask user for the cost of the item double cost = s.nextDouble(); //calculate the tax double tax = cost*TAX_RATE; //calculate total cost double total = cost+tax; System.out.println("Cost: " + cost); System.out.println("Tax : " + tax); System.out.println("Total: " + total); }

Exercises 1. Write a program that prompts the user for two integers and displays the sum, difference, product, and quotient of the numbers.